Heat-developable diazotype material



July 14, 1970 s, SHELER ET AL 3,520,691

HEAT-DEVELOPABLE DIAZOTYPE MATE IAL Filed March 15, 1967 7\ -LlGHT-SENSITIVE LAYER J WHEAT-SENSITIVE LAYER 3/ SUPPORT F\G. l

FIG. 2

' /LIGHTSENSITIVE LAYER |9- -fBARRIER LAYER l5 \IHEAT-SENSITIVE LAYER r SUPPORT F'KS. 3

F-LIGHT-SENSITIVE LAYER VSUPPORT (PERMEABLE) 25 HEAT-SENSITIVE LAYER FIG. 4

8mm 25 BYJOHANN MUNDER FlG. 5 my White.

ATTORNEY United States Patent 3,520,691 HEAT-DEVELOPABLE DIAZOTYPE MATERIAL Siegfried Scheler, Wiesbaden-Schierstein, and Johannes Munder, Wiesbaden-Biebrich, Germany, assignors, by mesne assignments, to Keuffel & Esser Company,

Morristown, NJ.

Filed Mar. 15, 1967, Ser. No. 623,340 Claims priority, application Germany, Mar. 19, 1966,

58,769 Int. Cl. G03c ]/60 US. Cl. 9675 6 Claims ABSTRACT OF THE DISCLOSURE A heat-developable diazotype material is prepared by including a heat-sensitive, alkali-generating beta-aminodicarboxylic acid with a two-component diazotype composition. Application of heat to such material provides alkaline environment conducive to dye-forming coupling of diazotype components.

BACKGROUND OF THE INVENTION Heat-developable two-component materials are known which carry, besides the light-sensitive layer, components which generate gaseous ammonia or volatile amines when heated. These substances penetrate into the light-sensitive layer, render it alkaline, and thus initiate the coupling process so that a dyestuit is formed. The various reproduction materials based on this principle which so far have become known differ in their alkalizing systems and in the position of the heat-sensitive layer with respect to the support and the light-sensitive layer.

It is known, e.g., to use salts or addition products of salts and bases which generate ammonia or volatile amines when heated. Further, compositions of finely divided ammonium salts and metal oxides have been used as thermolabile systems in heat-sensitive diazo materials. Urea has also been used as thermolabile substance yielding gaseous ammonia. Further, it has been suggested to use acid amides in admixture with slightly soluble inorganic bases in heatdevelopable reproduction materials. spending on the properties of the components used, the layers containing the substances which yield the volatile alkalies are arranged in the known materials in a specific position with respect to the light-sensitive layer and the support. Thus it is known to apply the heat-sensitive layer directly to the support and to coat it with the light-sensitive layer. When gas-permeable supports are used, the heat-sensitive layer is preferably applied to the back of the support. Further, it has been suggested to apply the heat-sensitive layer in the form of two separate layers and to dispose the substances capable of generating volatile alkali by reaction with each other separately in these two layers.

SUMMARY OF THE INVENTION Some of the heat-developable diazotype materials hitherto known yield copies of high quality, but none of them meets all the requirements to be met in practice to a fully satisfactory degree. Besides a high quality of the copies, it is required from a heat-developable diazotype material that the developing temperatures be as low and the developing times as short as possible. A temperature about 150 C. is to be considered as the upper limit for the developing temperature, because most supporting materials, in particular paper, suffer irreparable damages even by a short exposure to this temperature. The duration of heat action should not exceed one minute, because otherwise the apparatus required for development, normally a continuous working apparatus, will become too large.

Further, the storability of the materials is of decisive importance. Under normal atmospheric conditions, the materials should be capable of being stored for at least 6 months before a discoloration due to premature coupling becomes visible. This requirement particularly is not met satisfactorily by any of the hitherto known heatdevelopable diazotype materials.

It is an object of the present invention to provide a heat-developable diazotype material which can be developed at relatively low temperatures and by heat action of less than 1 minute and whose shelf-life is nevertheless satisfactory, even under tropical conditions.

The invention provides a heat-developable diazotype material which comprises a support, a light-sensitive layer, a heat-sensitive layer and, if desired, intermediate layers, and wherein the layers contain at least one diazo compound, one coupling component with acid additives and a component which generates a volatile base when heated, and, if desired, a binder, said substances being contained in the layers either individually or in admixture with each other. The material is characterized in that the heat-sensitive layer contains, as the component which generates a volatile base when heated, at least one beta-aminodicarboxylic acid or a monometal salt of such acid corresponding to the general formula wherein R stands for hydroxyl, alkyl, alkenyl, cycloalkyl, aralkyl or phenacyl groups which may be substituted,

R and R may be the same or difierent and stand for hydrogen, alkyl, alkenyl, cycloalkyl, or aralkyl groups which may be substituted, or R and R form an, optionally substituted, heterocyclic ring with the nitrogen atom to which they are attached.

A number of suitable beta-aminodicarboxylic acids and their decomposition temperatures are listed in the table below. The decomposition temperatures of these compounds range from about 70 to C., thus complying with the requirement that no temperatures higher than 150 C. must be applied during heat development. As a rule, the decomposition temperatures of the corresponding monometal salts are not very different.

The monosalts of alkali metals and alkaline earth metals and those of zinc and aluminum are preferred. It is not necessary to incorporate the metal salts themselves in the coating composition. The free beta-aminodicarboxylic acids may also be used with an alkaline compound of the metal. In the case of metals which form slightly soluble oxides, the free acids are preferably applied in admixture with the oxide. Strongly oxidizing or reducing oxides should not be used, however. Favorable results are obtained when the heat-sensitive layer contains zinc oxide in admixture with one or more free beta-aminodicarboxylic acids.

As has been found, the beta-aminodicarboxylic acids decompose under heat action in accordance with the following equation:

to yield alpha-substituted acrylic acids, ammonia or amine, and carbon dioxide. It is assumed that the carbon dioxide set free during the thermic decomposition of the compound acts as a propellant and thus causes a very quick penetration of the gaseous base into the light-sensitive layer. The above equation shows also why only the monosalts, and not the disalts, of beta-aminodicarboxylic acids are suitable. The disalts would not be capable of generating hydrogen and thus prevent the formation of the amine and the carbon dioxide.

A remarkable feature of the heat-developable diazotype materials with beta-aminodicarboxylic acids in the heatsensitive layer as substances which generate the volatile base is the wide range of variations in the arrangement of the heat-sensitive layer with respect to the other layers and in the combination of the single components. Thus, a material may be prepared as in FIG. 1, e.g., Whose heatsensitive layer 5 consists only of one or more beta-aminodicarboxylic acids of the above formula and a binder. In addition thereto, the layer 5 may also contain the coupling component, so that, in this case, the light-sensitive layer 7 contains only the diazo compound and the acid additives. Whereas in the hitherto known heat-developable diazotype materials the position of the heat-sensitive layer with respect to the support and the light-sensitive layer has normally been of critical importance, this is much less the case with the reproduction material of the present invention. The light-sensitive and the heat-sensitive layer may be in contact with each other, i.e. they may be disposed on the same side of the support as in FIGS. 1 and 2. This arrangement is preferred in the case of gas-impermeable supports, but it can be employed also with gas-permeable supporting materials. In order to prevent a weakening of the light striking the reproduction material, the heat-sensitive layer 5 is normally disposed as in FIG. 1, between the support 3 and the light-sensitive layer 7. With this arrangement, the heat-sensitive layer contains preferably free beta-aminodicar-boxylic acids. If monometal salts of beta-aminodicarboxylic acids are to be used, it is advisable to provide between the heat-sensitive and the light-sensitive layers 15, 17 (FIG. 3), an intermediate barrier layer 19 which consists either of a meltable or thermoplastic resin, of a wax, or of highly polymerized organic substances. The intermediate layer 19 should be thin enough to be penetrated by the gas which is generated. Normally, it should have a thickness of only a few microns.

If gas-permeable supports are used, the light-sensitive layer 27 and the heat-sensitive layer 25 are preferably disposed separately, on opposite sides of the support 23, as in FIG. 4. The gas generated by heat influence diffuses through the support into the light-sensitive layer. In this case, the light-sensitive layer 27 must contain the diazo compound and the coupling component. If the layer generating the volatile base is disposed on the back of the support, beta-aminodicarboxylic acids are preferably used which split off ammonia or aliphatic amines with high gas pressure when heated. Compounds in which the radicals R and R in the above general formula stand for hydrogen or alkyl groups having together not more than 8 carbon atoms are particularly suitable.

However, if compounds are to be used in which R and R stand for radicals with longer chains, or such compounds, in which these radicals combine with the nitrogen atom to which they are attached and form a heterocyclic ring, it is advisable to provide a further layer 29 of ammonium salts of strong mineral acids between the heatsensitive layer 25 and the back of the support 23, as in FIG. 5. Ammonium chloride and ammonium sulfate have proved to be particularly suitable salts for this purpose. The amine primarily set free from the beta-aminodicarboxylic acid liberates gaseous ammonia from the ammonium salt contained in this layer. This compound penetrates particularly easily through the support, initiates a fast coupling reaction, and thus causes for formation of a copy of high coloring power and brilliance.

Particularly favorable results are obtained when, in the structure of FIG. 5, the heat-sensitive layer 25 contains not only the free beta-aminodicarboxylic acid, but also zinc oxide. It is pointed out that when an intermediate layer 28 is employed which contains ammonium salts, even such beta-aminodicarboxylic acids may be used with good results in which the radicals R and R stand for alkyl residues with particularly long chains.

Suitable supports for the above described layers are sheet-like materials of very different nature. Paper supports are preferred. The paper used may be completely opaque or slightly transparent. Coated papers or plastic films, such as films of cellulose acetate, cellulose acetobutyrate, polyesters, cellulose hydrate or polyamides, may also be used. Woven and non-woven textiles may also be used, provided they are dense enough.

Preferably, the light-sensitive layer is a two-component layer of the kind customary in diazotype materials. It may contain any of the known combinations of diazo compounds and coupling components. Therefore, a preferred method for preparing the reproduction material of the invention consists in providing a commercially available diazotype material of the customary type, which normally would be developed by the action of ammonia, with an additional heat-sensitive layer 5', as in FIG. 2.

Suitable binders for the beta-aminodicarboxylic acids contained in the heat-sensitive layer are, inter alia: polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, formylpolyvinylacetal, butyryl polyvinylacetal, rice starch, and cellulose derivatives, such as carboxymethyl cellulose or ethyleellulose of medium viscosity. Depending on whether the layer is applied from a solution in water or an organic solvent, binders having the required solubility characteristics are selected. Alternatively, dispersions of the above-mentioned synthetic substances may be applied, in particular in connection with the preferred aqueous coatings.

The beta-aminodicarboxylic acids may also be dispersed or dissolved. Particularly good results are obtained with heat-sensitive layers on which the beta-aminodicarboxylic acids have been coated in disperse form. Therefore, beta-aminodicarboxylic acids of poor solubility may be used. The mixing proportions of binder and beta-aminodicarboxylic acid should be such that the heat-sensitive layer contains 0.25 to 1 part by weight of binder per part by weight of beta-aminodicarboxylic acid. Advanttageously, the weight of the heat-sensitive layer ranges from 2 to 3 g./m. However, values considerably above or below this range are also possible, depending on the composition and arrangement of the heat-sensitive layer.

The heat-developable diazotype material according to the present invention is prepared in known manner, using known techniques. As mentioned above, it is a preferred method to coat a normal two-component diazotype material suitable for dry-development on its back with a solution or dispersion containing the substance which generates the alkaline substance. It has proved to be advantageous, when applying this method, to add suitable additives to the heat-sensitive composition in order to prevent it from penetrating into the support and thus contacting the opposite layer. Auxiliaries suitable for this purpose are, e.g., aqueous dispersions of finely divided surface-active silica with an organic polymer as the binder. The layer is applied by means of known coating methods. The material is then dried at a temperature at least 20 C. below the point where the specific betaaminodicarboxylic acid used decomposes, splitting off an amine.

Processing of the diazotype material is simple and is done in the usual manner. After image-wise exposure of the reproduction material under a master, it is heated to temperatures above the decomposition temperature of the substance generating the volatile amine which is contained in the heat-sensitive layer, but not higher than 150 C. Preferably, such substances are applied which render it possible to develop the reproduction material at temperatures ranging from 90 to 130 C.

The time of exposure to the elevated temperature ranges from 5 to 30 seconds. Heating may be effected, e.g., by means of heated plates or rolls or by the application of infrared radiators.

The reproduction material of the present invention may also be used in a thermographic reproduction process, when the supports used are sufficiently thin and transparent. In this process, the copy is produced by the image-wise action of heat. Normally, a master with writing on one side is disposed between an infrared source and the reproduction material in such a manner that the surface of the master which carries the image is in contact with the heat-sensitive layer of the reproduction material. By the action of the infrared radiation, the darker image areas of the master are heated to a considerably higher degree than the lighter areas. In the case of the reproduction material of the invention, the degree of heating is suflicient to decompose the thermolabile substance. Advantageously, the copies prepared in this manner are fixed by a subsequent exposure to light, by which the unreacted diazo compound is destroyed. Otherwise, a second discoloration would take place when the material is exposed to a second heat treatment. The diiferent variations of the thermographic process known may also be performed with the reproduction material according to the invention.

Further, the diazotype material of the invention may be developed in known manner by the so-called dry process. For this purpose, it is image-wise exposed and then placed in an ammonia atmosphere, similarly to normal two-component diazotype material suitable for drydevelopment.

As stated above, the reproduction material according to the invention can be easily prepared and processed. It may be developed by a simple heating and yields copies with exceptionally good contrast. The outstanding storability of the material, which will be shown in detail in the following examples, deserves particular mention.

DESCRIPTION OF DRAWINGS The drawings schematically present various constructions of material of the present invention wherein:

FIGS. 1 and 2 show the sequence of layers employed with permeable or impermeable support sheets;

FIG. 3 shows the use of a thermoplastic barrier layer advisable when employing salts of the amino compounds of the invention;

FIG. 4 shows construction of material employing permeable supports; and

FIG. 5 shows the use of ammonium salts with heatsensitive layers including long chain amino compounds of the invention.

PREFERRED EMBODIMENTS Example 1 White base paper customarily used for diazotype purposes is precoated on one surface with an aqueous dispersion of finely divided silica and casein, dried, and then an aqueous solution of the following composition is applied to the same side:

Parts by weight Water Zinc chloride 3.75 Citric acid 2.50 Naphthalene-1,3,6-trisulfonic acid (sodium salt) 2.00 Thiourea 4.00

Saponine 0.02 2,3 dihydroxynaphthalene-6-sulfonic acid (sodium salt) 2.30 Zinc ehloride double salt of 4(N-ethyl-N-B-hydroxyethyl)benzene diazonium chloride 1.40

The sensitized paper is dried at a temperature between 70 and 80 C., and the back of the paper is then coated with a suspension obtained by grinding 10 parts by weight of (fl-N,N-dimethylamino-methyl)- benzyl-malonic acid 2 parts by weight of finely divided silica, and

parts by weight of toulene, in which 3 parts by weight Ethylcellulose T 200 (Hercules Powder Company, USA.) have been dissolved.

After drying at 45-55 C., a thin film is formed on the back of the paper in which the (fi-N,N-dimethylamino methyl)-benzylmalonic acid and the silica are finely dispersed.

The suspension is prepared by grinding the compounds in a ball or colloid mill until the ,B-aminodicarboxylic acid is pulverized to a particle size of about 5 to 15 A sheet of the diazotype paper prepared in this way is image-wise exposed under the master until the diazo compound has bleached out under the transparent areas of the master. The material is then contacted for a short time with rolls or plates maintained at a temperature of -135 C. A color is formed in the unexposed areas of the paper. The copy thus obtained is very rich in contrast and shows a strong, dark-blue azo dyestufr image on a clear white background. The unexposed diazotype paper can be stored up to three days at a relative humidity of 65% and a temperature of 42 C., without coupling taking place. A weak discoloration can be observed only after three days. This means that the material can be stored considerably longer than 6 months under normal climatic conditions.

Example 2 A base paper customarily used in diazotype processes is precoated on one surface with an aqueous dispersion of finely divided silica and casein, dried, and then coated, on the same side, with an aqueous solution of the following composition:

Parts by weight The sensitized paper is dried in the normal manner and the back of the paper is then coated with a suspension of the following composition:

Parts by Weight (,8-N,N-diethylamino-methyl) p methoxy benzylmalonic acid h Finely divided silica 2 Aqueous polyvinyl acetate dispersion (Mowilith DMC 2Farbwerke Hoechst A.G.) Water 100 The paper is again dried in an air current at 5055 C., and a thin film of polyvinyl acetate is formed on the back in which the p-aminodicarboxylic acid and the silica are finely dispersed.

The suspension is prepared by grinding in a ball or colloid mill.

A sheet of the diazotype paper thus prepared is exposed under a master and developed as described in Example 1. A copy produced shows a strong, dark blue image on a clean white background. The material can be stored for 3 days at a relative humidity of 65% and a temperature of 42 C., and weak coupling effects can be observed only after this period of time. This proves that the shelf-life of this material at normal temperature is sufiicient.

Example 3 Normal diazotype base paper which has been precoated as described in Examples 1 and 2 is coated with a solution containing:

Parts by weight Water -s 80 Citric acid 2.5 Zinc chloride 3.75

Naphthalene-1,3,6-trisulfonic acid (sodium salt) 2.00

Thiourea 4.00 Saponine 0.02 2,3-dihydroxynaphthalene-6-sulfonio acid (sodium salt) 2.3 Zinc chloride double salt of 4,N,N-diethylamino-.

benzene diazonium chloride s 1.4

and dried in the usual manner. Then the material is coated on its back with a solution of 100 parts by weight of water and 30 parts by weight of ammonium sulfate,

8 3 parts by weight of Ethylcellulose T 200 (Hercules Powder Company, U.S.A.) have been dissolved.

When the material is dried at a temperature of 45- 50 C., a thin film forms on the back of the paper in which the fl-amino-dicarboxylic acid, the silica and the talcum are dispersed in a fine distribution.

A sheet of the diazotype material prepared in this manner is image-wise exposed under a master and developed as described in Example 1. The copy produced shows an extremely strong, dark blue image on a white background. A copy prepared on the same material by development with gaseous ammonia shows an image in the same color. The material can be stored for 2 /2 days at a relative humidity of 65% and a temperature of 42 C., practically no coupling taking place, and is thus sufiiciently storable at temperatures around 20 C.

Example 4 White base paper customarily used for diazotype processes is precoated on one surface with an aqueous dispersion of finely divided silica and polyvinyl acetate and the same side is then coated with an aqueous solution having the following composition:

Parts by weight Water Citric acid 1.2 Zinc chloride 1.1 Aluminum sulfate 05 Naphthalene-1,3,6-trisulfonic acid (sodium salt) Thiourea 2.5 Saponine 0.02 Isopropanol 2.0 Zinc chloride double salt of 4-morpholino-2,5-diethoxy-benzene-diazonium chloride 1.2 1[(2 N,N diethylamino) carbanilido]-3,5dihydroxy 4-bromo-benzene 1.2

The sensitized paper is dried in the usual manner and the back of the paper is then coated with a suspension prepared by grinding 10 parts by weight of (ti-N,N-diethylamino-methyl)- benzyl-malonic acid, and

4 parts by weight of talcum in parts by weight of toluene, in [which 3 parts by weight of Ethylcellulose T 200 (Hercules Powder Company, U.S.A.) have been dissolved.

The paper thus produced is dried at 35-40 C. in an air current.

A sheet of the highly light-sensitive diazotype paper thus prepared is image-wise exposed and then contacted for a short time with rolls or plates heated to a temperature of C. The copy thus produced is exceptionally rich in contrast and shows a strong, slightly bluetinged red image on a clear white background. The unexposed diazotype material may be stored up to 3 days at a relative humidity of 65% and a temperature of 42 C. with practically no coupling taking place, and thus possesses good storability under normal conditions.

Example 5 A transparent paper customarily used for diazotype purposes is precoated with a suspension prepared by grinding 5 parts by weight of (fl-N,N-di-n-propylamino-methyl) benzyl-malonic acid,

2 parts by weight of phloroglucinol carboxylic acid, and

2 parts by weight of 'y-resorcylic acid in 100 parts by weight of ethyl acetate, in which 3 parts by weight of Ethylcellulose T 200 (Hercules Powder Company, U.S.A.) have been dissolved.

9 The precoated paper is dried at 30-40 C. in an air current and then a solution of the following composition is applied to the same side:

Parts by 'weight Citric acid 1.5

Polyvinylacetate CT (Far-bwerke Hoechst A.G.) 2.5

Ethanol 50.0

Water 20.0 Zinc chloride double salt of 4-N-ethyl-N-3-hydroxyethyl benzene-diazonium chloride 1.5

Example 6 A transparentized paper customarily used as support in diazotype processes is coated with a suspension which was prepared by grinding 5 parts by weight of (B-N,N-dimethylamino-methyl)- benzyl malonic acid,

2 parts by weight of pholoroglucinol carboxylic acid, and

2 parts by weight of 'y-resorcyclic acid in 100 parts by weight of ethyl acetate in which 3 parts by weight of Ethylcellulose T 200 (Hercules Powder Company, U.S.A.) have been dissolved.

The precoated paper is dried in an air current at 3040 C. and the same side is then provided with a solution of 3 parts by weight of Ethylcellulose T 200 (Hercules Powder Company, USA.) in 100 parts by weight of ethyl acetate,

and again dried at 30-40 C. A solution of Parts by weight Citric acid 2 Methylcellulose having a viscosity of cps. at C.

Ethanol 50.0

Water 20.

Zinc chloride double salt of 4,N,N-diethyl-aminobenzene diazonium chloride 2.0

is then applied to the already twice precoated side of the paper and dried at 5055 C. in an air current.

An original with writing on one side is placed in a thermographic copying apparatus between the infrared source and the diazotype material in such a manner that the written side of the original is either in contact with the light-sensitive layer of the diazotype material or with the side opposite the light-sensitive layer of the diazotype material. The undecomposed diazo compound is destroyed by subsequent exposure to light. A strong, brown-black copy is obtained. The dyestuif formed in the image areas is impermeable for ultraviolet light, so that the copy may be used as intermediate original from which further copies may be produced on diazotype material.

Example 7 A base paper customarily used in diazotype processes is precoated with a suspension obtained by grinding 10 parts by weight of (fi-N,N-dimethylaminomethyl)- ethyl-malonic acid,

3 parts by weight of finely divided silica,

6 parts by weight of polyvinyl acetate dispersion (Mowilith DC--Farbwerke Hoechst) in 100 parts by weight of water 10 and then dried at 50-60 C. in an air current. To the same side of the precoated material, an intermediate layer is applied which contains parts by weight of water 10 parts by weight of polyvinyl acetate dispersion (Mowilith DMC 2Farbwerke Hoechst AG.) and 3 parts by weight of finely divided silica.

The material is again dried at 5060" C. and upon the thus twice precoated side of the paper, a solution is applied which consists of Parts by weight Water 80 Citric acid 1.5 Tartaric acid 1.0 Zinc chloride 4.0 Naphthalene-1,3,6-trisulfonic acid (sodium salt) 2.5 Thiourea 4.0

Saponine 0.02 2,3-dihydroxynaphthalene-6-sulfonic acid (sodium salt) 2.3 Zinc chloride double salt of 4-(N-ethyl-N-fi-hydroxyethyl)-benzene-diazonium chloride 1.4

and then dried in the usual manner.

A sheet of the diazotype paper prepared in this manner is image-wise exposed and then contacted for a short time with rolls or plates heated to -115 C. The copy thus obtained is very rich in contrast and shows a strong, dark blue image on a pure white background.

Example 8 White base paper customarily used for diazotype purposes is precoated on one side with an aqueous dispersion of finely divided silica and casein, dried, and the same side of the paper is then coated with an aqueous solution of the following composition:

Parts by weight Water 100 Citric acid 3.1 Zinc chloride 4.6 Naphthalene-1,3,6-trisulfonic acid (sodium salt) 2.5 Thiourea 5.0 Saponine 0.02 Alizarin Irisol RL 0.02 2,3-dihydroxynaphthalene-6-sulfonic acid (sodium salt) 2.8 Zinc chloride double salt of 4-(N-ethyl-N-fl-hydroxyethyl)-benzene-diazonium chloride 1.35

The sensitized paper is dried in the usual manner and the back of the paper support is then coated with a solution of the following composition:

Parts by weight Water 100 flN,N-dimethylaminomethyl -benzyl-malonic acid 10 Sodium bicarbonate 3.34 Carboxymethylcellulose (cp. 10/ 20 C.) 4.00

The paper is again dried at 5055 C.

A sheet of the diazotype paper thus prepared is imagewise exposed under a master and then contacted for a short time with rolls or plates having a temperature of -130 C. The copy thus produced is rich in contrast and shows a dark blue azo dyestufi image on a white background.

Example 9 One side of a base paper customarily used for diazotype purposes is precoated with an aqueous dispersion of finely divided silica and casein, dried, and the same side of the material is then coated with an aqueous solution having the following composition:

Naphthalene-1,3,6-trisulfonic acid (sodium salt) 2.5 Thiourea 5.0 Saponine 0.02 Alizarin Irisol RL 0.02 2,3-dihydroxynaphthalene-6-sulfonic acid (sodium salt) 2.6 Zine chloride double salt of 4-N,N-dimethylaminobenzene diazonium chloride 1.35

The sensitized paper is dried in the usual manner and the back of the paper is then coated with a solution obtained by dissolving Example 10 One side of a white base paper of the kind customarily used in diazotype processes is precoated with an aqueous dispersion of finely divided silica and polyvinyl acetate and the same side of the material is then coated with an aqueous solution of the following composition:

Parts by weight Water 100 Citric acid 1.7 Zinc chloride 3.45 Aluminum sulfate 0.85 Thiourea 5.75 Saponine 0.02 Alizarin Irisol RL 0.02 2,7-dihydroxynaphthalene-3,6-disulfonic acid (sodium salt) 1.7

Zinc chloride double salt of 4-N-morpholino-2,5-diethoxy-benzene diazonium chloride 1.2

The sensitized paper is dried in the usual manner and the back of the paper is then coated with a suspension obtained by grinding Parts by weight (13-N,N-dimethylamino-methyl -benzyl-malonic acid 10 Zinc oxide Finely divided silica 2 Carboxymethylccllulose cp./ C.) 2.5 Polyvinylacetate dispersion (Mowilith DMC 2- Farbwerke Hoechst A.G.) 4 Water 100 The paper thus obtained is dried at 5560 C.

A sheet of the highly light-sensitive diazotype paper thus produced is image-wise exposed and then shortly contacted with rolls or plates heated to 125130 C. The copy obtained is exceptionally rich in contrast and shows a strong, dark blue image on a 'white background. The unexposed diazotype material may be stored for 3 days without coupling at a relative humidity of 65% and a temperature of 42 C; at a relative humidity of and a temperature of 20 (3., it can be stored for half a year.

. 12 Example 11 A base paper of the kind customarily used in diazotype processes is precoated with an aqueous dispersion of the following composition:

Parts by weight Water Ammonium chloride 20 Finely divided silica 5 Polyvinyl acetate dispersion (Mowilith DMC 2 Farbwerke Hoechst A.G.) 4

After drying, the same side of the material is sensitized by means of the solution used in Example 8, dried again, and then the back of the paper is coated with the aqueous suspension used in Example 2. The coated paper is then dried at 55-60 C.

A sheet of the diazotype paper thus produced is imagewise exposed in the normal manner and then brought into contact with rolls or plates having a temperature of C. The copy thus produced shows a strong, bluishblack image on a white background.

The above examples have been presented for the purpose of illustration and should not be taken to limit the scope of the present invention. It will be apparent that the described examples are capable of many variations and modifications which are likewise to be included within the scope of the present invention as set forth in the appended claims.

What is claimed is:

1. Heat-developable diazotype material comprising:

(a) a support;

(b) a light-sensitive layer on said support comprising a light-sensitive diazonium compound and an acidic stabilizing compound;

(c) a heat-sensitive layer on said support comprising a heat-activatable generator of an alkaline material, said generator being a compound consisting of the group of beta-aminodicarboxylic acids, and metal monosalts of such acids, said acids having the general formula wherein R is hydroxy, alkyl or alkenyl having 1 to 8 carbon atoms, cyclohexyl, phenyl alkyl, alkoxy phenyl alkyl or phenaeyl, R is H, alkyl or alkenyl having 1 to 4 carbon atoms, R is H, alkyl or alkenyl having 1 to 4 carbon atoms, cyclohexyl or benzyl, or R and R form a hydrogenated 5- or 6-membered N-heterocyclic ring; and (d) an azo dye coupler capable of forming a dye with said diazonium compound in an alkaline medium, said coupler being in one of said light-sensitive or heat-sensitive layers.

2. Material according to claim 1 wherein said lightsensitive layer comprises an outermost layer on at least one side of said support.

3. Material according to claim 1 wherein said support is gas-permeable and said light-sensitivelayer, and said heat-sensitive layer are disposed on opposite sides of said support and said coupler is present in light-sensitive layer.

4. Material according to claim 3 wherein said generator is a free acid and wherein a layer of an ammonium salt of a mineral acid is disposed between said support and said heat-sensitive layer.

5. Material according to claim 1, wherein said lightsensitive layer, is disposed on the same side of said support as said heat-sensitive layer, and wherein said generator is a metal monosalt. said coupler is present in said light sensitive layer and a barrier layer of thermoplastic material is disposed between said light-sensitive and heatsensitive layers.

6. Material according to claim 1, wherein said generator is selected from said group of acids, including in said heat-sensitive layer about 1 part of zinc oxide for each part of said acid.

References Cited UNITED FOREIGN PATENTS 907,724 10/1962 Great Britain. 1,418,156 10/1965 France.

6404649 10/ 1964 Netherlands.

5 OTHER REFERENCES Review, February 1962, pp. 14, 15, 22 and 26. STATES PATENTS Klimkowski et a1 96 9l XR 10 NORMAN G. TORCHIN, Primary Examiner Lawton et a1 9649 XR C. BOWERS, Assistant Examiner Kashiwabava 9649 Meijs et a1 9649 XR US. Cl. X.R. Tummers 9691 XR Munder et a! 15 9649, 25065.1, 117-368, 36.9

Dietzgen, J. E., A Thermal Diazo Primer, Reprod. 

